Field emission display (“FED”) systems are well-known to those of ordinary skill in the art. FED technology represents one alternative means for providing relatively high-resolution displays for personal computers and the like, such as may also be provided by existing liquid crystal display (“LCD”) technology.
Briefly characterized, present FED systems are most commonly implemented in the form of a plurality of discrete, selectively controllable cathodoluminescent devices arranged in an array so as to be able to present a viewable image comprising a plurality of individual picture elements (“pixels”). Known FED technology often utilizes semiconductor material (e.g., silicon) as a substrate to build active-matrix field emission displays (“AMFEDs”). An example of a known FED system is described in U.S. Pat. No. 5,894,293 to Hush et al., entitled “Field Emission Display Having Pulsed Capacitance Current Control.”
Due to, among other factors, physical dimension and fabrication processing considerations, a recognized issue in the implementation of FEDs is that of uniformity among the many discrete cathodoluminescent devices making up a functional display. That is, those of ordinary skill will appreciate that one or more operational parameters of semiconductor devices, such as the conductivity of a FET transistor or the behavior of a cathodoluminescent emitter tip, for example, may vary from device to device or pixel-to-pixel as a result of practically unavoidable variations in such characteristics as the size, shape, doping concentrations, and so on, of each individual device. As will hereinafter be described in further detail, FEDs are typically made up of a large number—perhaps up to many hundreds of thousands or even millions—of cathodoluminescent structures each having one or more features as small as 50 Angstroms. Commercial-scale fabrication of such structures with acceptable physical and electronic uniformity among their number is a known engineering challenge.
A further aspect of FED technology of relevance to the present disclosure is the potential applicability of FED technology to the field of infrared radiation detection and imaging. Specifically, it has been proposed by one or more of the present inventors that infrared radiation-sensitive elements may be incorporated into FED systems to provide infrared detection and imaging capabilities. For example, it has been proposed to incorporate infrared-sensitive components into a FED system in order for such system to be responsive to impinging infrared radiation to display a graphical image reflecting the presence and intensity of the infrared radiation. Those of ordinary skill in the art will appreciate that such capabilities have potential application in, by way of example but not limitation, so-called “night-vision” equipment.
In embodiments of FED systems incorporating infrared-sensitive elements as proposed by the present inventors, an array of cathodoluminescent elements may be rendered responsive to the presence and intensity of impinging infrared radiation and thereby present a graphical image reflecting the infrared radiation.
Whereas conventional FED systems are susceptible to potentially unacceptable deficiencies relating to the problems of uniformity among the individual cathodoluminescent elements of which they are comprised, FED systems which additionally incorporate infrared-sensitive elements giving the systems additional capabilities and functionality are even more susceptible to uniformity problems. The additional infrared-sensitive elements are vulnerable to processing variation to an extent comparable to the elements comprising conventional FED systems. Moreover, the fabrication processes used to incorporate infrared-sensitive elements into a FED system can themselves worsen the problems with processing variations.
One proposed manner of addressing the problems of non-uniformity among a plurality of cathodoluminescent devices in a FED system involves providing external circuitry for adjusting, on a pixel-by-pixel basis, the voltage levels of the signals used to access each pixel. By adjusting the access voltage level individually for each pixel, the current through each cathodoluminescent element can be controlled. Non-uniformity in the performance among the plurality of cathodoluminescent devices can thus be compensated for with appropriate pixel-by-pixel adjustment.
In some cases, it may be undesirable to require external circuitry to compensate for non-uniformity in FED pixels. At the least, such circuitry is likely to increase the size, cost, complexity, and power consumption of a FED or a FED IR sensor. Furthermore, the digital signal processing overhead incurred by such circuitry can adversely impact the FED's performance.